(I made my decision based upon the following article and U.S.A. brass!)

Neal

There is a great deal of interest in .338″ caliber cartridges for long range shooting. This is specifically due to high BC mass produced bullets available. While it takes a great deal of powder to push a 250gr to 300gr bullet at acceptable velocities for long range shooting, the performance has trumped the cost in the minds of many shooters (not to mention military and law enforcement world-wide). Recently, the most popular long range 338ís are the 338 Remington Ultra Mag, 338 Lapua mag, and 338 Edge. The first two are self explanatory, the Edge is a 338◊300 Remington Ultra Mag. It is most commonly referred to as the 338″EdgeĒ due to Shawn Carlock of Defensive Edge who is the biggest proponent of the cartridge and has, by far, the most experience with it. There are some other 338ís for long range, but Iíll mostly focus one these three for the sake of keeping this brief. These cartridges can be used in factory long actions and make a repeater Even when using long, high BC bullets, like the 300gr SMK!
One common misconception is that these cartridges are end all, be all, 1000yd lasers. While the 1000yd performance is excellent, there are much more efficient ways of getting equal and in some cases better ballistic performance at 1000yds and less. For example you could fire a 168gr Berger VLD from a 7mm mag at 3100fps and have an expected drop of 22.25 MOA and drift of 5.25 MOA for a 10mph cross-wind at 1000yds. A 338 Lapua mag firing a 250gr Scenar at 2960 would have a drop of 24.25 MOA and 5.25 MOA windage for the same range/conditions. A Lapua mag firing a 300gr SMK at 2850fps would have a drop of 25 MOA and 4.75 MOA windage for the same range/conditions. If you want to see how these 338ís stack up to other cartridges, run the numbers through a ballistic calculator. For those who take large game at or near 1000yds the energy provided by these cartridges is ideal. Where the 338ís really shine ballistically is well beyond the 1000yd mark. They have been used effectively and with accuracy out to 1 mile (1760yds) and beyond. Two of the major obstacles to shooting at extreme range are going sub-sonic (or even trans-sonic) and wind drift. A major part of the solution to both of these, is a higher than usual BCís. Letís consider some of the long range bullets available for the 338ísÖ
250gr Sierra Match king BC: .587 (above 2150fps) .606 (between 2149 and 1700fps)
250gr Lapua Lock Base BC: .662
250gr Lapua Scenar BC: .675
300gr Sierra Match king BC: .768
The popularity of this caliber will only insure that more high BC bullets will be developed in the future. Berger will be releasing two new bullets for the .338″, one of which is rumored to weigh 300gr and have a BC of around .855!
There is great debate about the velocities these cartridges can produce in relation to each other. I do not have the resources available to build and compare each of these cartridges with identical components so weíre left to speculate on what info is available. My Sierra Reloading Manual uses a 26″ test barrel for both the 338 RUM and the 338 Lapua. It gives essentially identical maximum velocities for the bullets in question, although the RUM was reaching them with a higher percentage of the powders tested. This seems counter intuitive because the capacities of these cartridges are virtually the same and the Lapua is rated at a maximum pressure of 69,000 psi, while the RUM is rated at a maximum of 64,500 psi (Vihta Vuori Reloading manual). I canít confirm what pressures Sierra used to test these cartridges, but the data is scientifically acquired. The respective velocities of factory loaded ammo for these two cartridges would suggest that the Lapua has the velocity advantage. There is much debate in internet forums of how these cartridges stack up. The most popular consensus (from what Iíve gathered) is the 338 Edge is the fastest followed by the Lapua mag, with the 338 RUM not too far behind. I would argue that this is the most sensible conclusion since it follows the general capacity/pressure model (please do not take this to mean I view forum opinions as scientific data). The debate is somewhat irrelevant, since weíre talking about a spread of less than 100fps between them. The barrelís design and length could possibly have a greater impact of MV than the cartridge itself. If youíre like me, the fastest load you test for a particular cartridge may not be the one you use. Other factors weigh in like accuracy (low ES and SD) as well as temperature sensitivity etc. It would be difficult to speculate what cartridge would provide the highest velocity while remaining ďaccurateĒ.
Many wonder about how long a barrel should be for these cartridges. From what I can gather 28″-30″ is about optimal. This gives you the MVís you expect and allows you to keep the weight manageable. Some have used up to 34″ barrels and are claim higher MVís and better ballistic performance. Iíve heard that going from 28″ to 30″ only nets and extra 50fps. It may not seem like much for the weight of two inches of barrel. For some it may be worth it. Depending on how far you want to shoot your rifle, an extra 50fps could be just what you need. If 28″ barrels and the weight that comes with them is unattractive to you, Iíd recommend looking into other cartridges (or re-evaluate your long range goals). There is no point in wasting powder in the form of muzzle blast. These are large cartridges that use slow burning powders and require long barrels.
The biggest difference in my opinion between these cartridges is reloading cost. Theyíll use around the same amount of powder, and the bullets are the same, but the brass is another story. Brass for the Lapua is commonly found for around $195 for 100pc. The 338 RUM, and 338 Edge (wich uses 300 RUM brass) can be had for around $80 for 100pc. This is a big difference in reloading cost, although a straight across comparison would probably not be fair to the Lapua. Itís quite likely that the Lapua brand brass (one of only two brands currently available for the 338 Lapua) would last a couple more firings compared to the others. Itís also notable that to build a rifle in 338 lapua a standard magnum bolt face would not work, requiring a little more work by your gun smith (my smith only charged me around $30 for this, but your mileage may vary). The 338 Edge definitely gives the most bang for your buck. Some claim the Lapua is more accurate. If this has any merritt, itís likely due to higher brass quality available for the Lapua. If one does a quick search youíll quickly find excellent long range accuracy can be had by the RUM and Edge. It is my opinion that the smith you select to build your rifle, will by far have the greatest influence of the accuracy potential. That being said, I personally use Lapua brass when itís available for a cartridge Iím loading.
Some other 338 cartridges that may catch your attention and deserve your consideration include: 338◊378 Wby mag, 338 Kahn, 338◊416 Rigby Improved, 338 Snipe Tac, 338 Allen Magnum, 338 Titan, and others. Any of these will ballistically outperform the RUM, Lapua, and Edge.